Operating Systems Lecture 3: Process Concept

Questions and Answers

What is a process?

A program in execution.

Which of the following are parts of a process?

Data section (correct)

Heap (correct)

Program code (correct)

Current activity (correct)

File metadata

A program is a _____ entity stored on disk.

passive

A process can have multiple program counters.

True Signup and view all the answers

What does the state 'Running' mean for a process?

Instructions are being executed. Signup and view all the answers

What does the 'Waiting' state indicate?

The process is waiting for some event to occur Signup and view all the answers

What is contained within a Process Control Block (PCB)?

Process state, program counter, CPU registers, scheduling information, memory-management information, accounting information, I/O status information. Signup and view all the answers

What is the goal of process scheduling?

Maximize CPU usage Signup and view all the answers

A context switch occurs when the CPU switches from one process to another.

True Signup and view all the answers

Study Notes

Process Concept

Operating systems execute various programs as processes, which are programs in execution.
A process must progress sequentially; no parallel execution of instructions occurs within a single process.
Key components of a process include:
- Program Code (Text Section)
- Current Activity: Includes program counter and processor registers.
- Stack: Stores temporary data such as function parameters, return addresses, and local variables.
- Data Section: Contains global variables.
- Heap: Memory allocated during runtime dynamically.

Process Activation

A program remains passive when stored on disk (executable file); it becomes an active process when loaded into memory.
Program execution can start from GUI mouse clicks or command-line entries.
One program can have multiple processes, allowing for concurrent users accessing the same application.

Process State

Processes shift between various states as they execute:
- New: Process is being created.
- Running: Instructions are actively executed.
- Waiting: Process waits for an event to occur.
- Ready: Process is prepared to be assigned to a processor.
- Terminated: Process has completed execution.

Process Control Block (PCB)

PCB contains vital information about each process, also known as the task control block.
Key elements within PCB include:
- Process State: Indicates current status (e.g., running, waiting).
- Program Counter: Points to the next instruction to execute.
- CPU Registers: Holds values of all process-centric registers.
- CPU Scheduling Information: Contains priorities and scheduling queue pointers.
- Memory-Management Information: Details memory allocated to the process.
- Accounting Information: Tracks CPU time used, elapsed clock time since process start, and time limits.
- I/O Status Information: Lists I/O devices allocated to the process and open files.

Threads in Processes

Initially, processes have a single thread of execution.
Multiple threads of control can be created, requiring storage for additional program counters in the PCB.

Process Scheduling

The process scheduler is responsible for selecting the next process for CPU execution.
Goals include maximizing CPU usage and maintaining scheduling queues:
- Ready Queue: Includes processes in main memory that are ready and waiting for execution.
- Wait Queues: Includes processes waiting for I/O or other events.
Processes transition between various queues as they execute.

Queueing Diagram Representation

Commonly visualized through queueing diagrams illustrating the flow of jobs between the ready queue, CPU, and I/O queues.
Illustrates how processes interact with CPU and handle I/O requests.

Context Switching

Occurs when the CPU transitions from executing one process to another.
Involves saving the current process state into its PCB and loading the state of the next process.
Context switches can occur due to interrupts or system calls.